In the field of ophthamology, there are certain symptoms, such as a burning sensation, dryness or excessive wetness around the area of the eye, which may indicate obstruction of the channels which normally serve to drain or discharge moisture from the surface of the eyeball.
The moisture for the eyeball is produced by the tear glands, mostly above and behind the upper eyelids. The tear flow down across the eyes and the moisture collects at the margins of the eyelids. From there the accumulation of fluid flows toward the corner of the eye, adjacent the nose, where the upper punctum and the lower punctum each provide a drain orifice which leads to a sac common to both punctae. The sac has a discharge opening leading into the naso-lacrimal duct, which, in turn, discharges the drained moisture into the nose passages, where it normally evaporates. The combination of punctum, sac and duct comprise the normal outflow channel for the moisture normally supplied to the eyeball by the tear ducts. The patency or openness of this channel determines the efficacy of the moisture drainage from the eye.
When the channel becomes partially or wholly obstructed for any reason, discomfort may occur and result in certain symptoms, such as aforementioned, which make it desirable to test the patency of the tear outflow channel to determine if, in fact, it is not providing adequate moisture outflow.
The method that currently is most favored for testing patency is the "Jones test" which utilizes a fluorescein dye. A drop of the dye is applied to the eyeball and the change in concentration of the dye on the eyeball is visually observed over a time span which may range up to fifteen minutes, depending on the patency of the outflow channel and the quantity of moisture produced by the tear ducts. Ordinarily, the observation time is 5-10 minutes. If there is adequate patency, there is a visually determinable change in the observed concentration of the dye over a relatively short time span. If obstruction exists, the change in concentration occurs, if at all, much more slowly. Understandably, it takes considerable skill and experience for the observer to correctly interpret the observed changes in the concentration of the dye.
Alternatively, the nostril of the nose is packed with tissue or other soft, absorbent material before the dye is applied to the eyeball. Then, after a given period of time, e.g. seven minutes, the packing is removed and exposed to a cobalt blue light to determine the absence or presence of the fluorescein dye and attempt to determine about how much has traveled from the eye into the nose, as a measure of patency.
If it is concluded, as a result of the foregoing procedure, that an obstruction exists in the outflow channel, then more accurate and sophisticated procedures, such as radio-active injection of the punctum, are available for establishing the specific location and character of the obstruction.
Regardless of which variation or combination of the fluoroscein dye test is utilized, it is time-consuming, and its interpretation can be as wide-ranging and indeterminate as the subjectiveness and experience of the observer warrants.